New model to predict thermomagnetic properties of nanostructured magnetic compounds

The development of new materials showing the magneto-caloric effect (MCE) requires fast and reliable characterization methods. For this purpose, a phenomenological model developed by M. A. Hamad has proven to be a useful tool to predict the magnetocaloric properties (the isothermal magnetic entropy change, Δ S _M , the magnetization-related change of the specific heat, Δ C _P,H , and the relative cooling power, RCP) via calculation from magnetization measurements as a function of temperature, M(T) . However, fitting the M(T) data is difficult for broad, smoothed-out transition curves which are often observed for material systems such as core-shell nanoparticles, nanowires, nanowire fabrics or nanoparticle hybrid materials. Thus, in this contribution we present a different approach enabling proper fitting of such magnetization data via the use of the asymmetric Boltzmann sigmoid function. As examples, we present fits to M(T) curves of polycrystalline, bulk La _0.67 Ba _0.33 MnO ₃ as well as La _1-x Sr _x MnO ₃ (x = 0.2, 0.3, 0.4) and La _0.7 Ca _0.3 MnO ₃ nanostructured materials from various authors.